Regulation of gene expression in bacteria occurs frequently at the level of transcription. RNA polymerases which transcribe these genes are composed of a multi-subunit core enzyme and an additional protein, or sigma factor, which permits the whole enzyme to recognize promoter elements and initiate transcription at these specific sites. Cells contain multiple sigma factors and their relative levels in the cell provide a fundamental control of gene expression.
Bacillus subtilis has at least 10 different sigma factors. Haldenwang, W. G. (1995) The sigma factors of Bacillus subtilis. Microbiological Reviews 59, 1-30. Sigma-B is activated to direct the transcription of a subset of genes when B. subtilis stops exponential growth or is subjected to a number of environmental stresses (e.g., heat, salt, ethanol and peroxide). Boylan, S. A., Redfield, A. R. & Price, C. W. (1993) Transcription factor sigma B of Bacillus subtilis controls a large stationary-phase regulon. Journal of Bacteriology 175, 3957-63; Boylan, S. A., Redfield, A. R., Brody, M. S. & Price CW. (1993) Stress-induced activation of the sigma B transcription factor of Bacillus subtilis. Journal of Bacteriology 175, 7931-7.
Staphylococcus aureus, is a pathogen related to Bacillus species. In the host, S. aureus cells are exposed to a range of environmental stresses, some analogous to those mentioned above. Furthermore, bacterial populations in infection loci are likely to contain slow or non-growing bacteria. Thus an equivalent of sigma-B is likely to play a crucial role in the adaptation of S. aureus to the host environment.
At least four proteins are known to regulate sigma-B. Three (RsbV, RsbW and RsbX) are the products of genes which are co-transcribed with the structural gene for sigma-B (sigB). The fourth (RsbU) lies immediately upstream of the RsbV gene. RsbW binds to sigma-B, blocking sigma-B-dependent transcription. RsbV can form a complex with RsbW and reduce the sequestration of sigma-B by RsbW. Additionally RsbW is able to phosphorylate RsbV to a form which is unable to interact with RsbW. Dufour, A. & Haldenwang, W. G. (1995) Interactions between a Bacillus subtilis anti-sigma factor (RsbW) and its antagonist (RsbV) Journal of Bacteriology 176, 1813-20. RsbU, directly or indirectly, facilitates the RsbV-dependent release of sigma-B from RsbW. Voelker, U., Dufour, A. & Haldenwang, W. G. (1995) The Bacillus subtilis rsbU gene product is necessary for RsbX-dependent regulation of sigma B. Journal of Bacteriology 177, 114-22.
Clearly, there is a need for factors that may be used to screen compounds for antibiotic activity and which may also be used to determine their roles in pathogenesis of infection, dysfunction and disease. There is a need, therefore, for identification and characterization of such factors which can play a role in preventing, ameliorating or correcting infections, dysfunctions or diseases.
The polypeptide of the present invention has amino acid sequence homology to known regulator of a sigma factor.